1. Field of the Invention
The present invention relates to a linear motion guide unit in which a slider is movable on an elongated track rail by virtue of rolling elements running through recirculating passages where separating elements are each arranged between any adjacent rolling elements to keep the rolling elements against coming in engagement with each other.
2. Description of the Prior Art
In most linear motion guide units, the rolling elements run through the recirculating passages in the slider to allow the slider to move on the track rail. Nevertheless, any adjacent rolling elements can sometimes come into contact with each other when they run through the load areas provided between the track rail and the slider. Especially, the rolling elements in the linear motion guide units, as having neared each other, can sometimes come into contact or engagement with each other because a distance of the centers of adjacent rolling elements changes subtly owing to the eccentricity of each rolling element, the skew and deformation of the track rail, which might arise from external loads applied unevenly. As the rolling elements turn in the same direction, the contact forces at contact areas on one rolling element are opposite the contact forces on the other. Thus, the frictional forces arising from the contact or engagement of the adjacent rolling elements results in impeding the smooth running of the rolling elements. During sliding motion of the slider on the track rail, the rolling elements in the recirculating passages are subjected to the repeated collisions against one another as well as the raceways, and moreover the rolling is substituted frequently for sliding motion. This causes noise or vibration considerably high in frequency and consequently premature wear of the rolling elements as well as the recirculating passages, thus reducing the operating accuracy and the acceptable service life of the linear motion guide unit.
A linear motion guide unit has been conventionally proposed, in which separators are each arranged between any two adjacent rolling elements to keep the rolling elements from coming into direct contact with each other in the recirculating passages. Referring to FIG. 10, there is shown an example of the prior separators. A separator 50 in FIG. 10 is made in a substantially cylindrical form and provided in axially opposite faces thereof with semi-spherical concavities 51, which are arranged in symmetry to each accommodate a part of the sphere of any rolling element 20. Any separator 50 has to be accepted commonly to isolate any two adjacent rolling elements 20 apart from each other, so that an axial distance between the centers of the semi-spherical concavities 51 is preselected to a fixed thickness t.
When the slider moves on the track rail, the rolling elements run through the recirculating passages, which are composed of non-loaded areas formed in the slider and load areas provided between first raceway grooves on the track rail and second raceway grooves on the slider. Most recirculating passages usually show some variance in length. Thus, when each of the separators 50 shown in FIG. 5 is in turn interposed between any two adjacent rolling elements or balls 20, the last separator can be sometimes interposed either too tightly or too loosely. Nevertheless, it is very tough to make the recirculating passage match in length with a circular string of the combined rolling elements and separators. Any separator cramped tightly can afford no play to the associated adjacent rolling elements, thereby increasing remarkably the sliding friction applied to the slider. To cope with this, it may be propose to prepare other types of the separators for the last separator, which are different in thickness t from the major separators to compensate for the variance in length of the recirculating passage. However, this needs to reserve many types of the separators differing in their axial thickness, resulting in disadvantages of complicated production and management of parts or components, which might cause the increase of production cost of the linear motion guide unit.
With the use of the separators having a fixed axial thickness, the rolling elements can sometimes dent the track rail with pitches nearly equal to that of the rolling elements. Thus, the slider can get scratched thereby resulting in causing noise, unacceptable vibration and badly premature wear. To deal with the disadvantage mentioned just above, a linear motion guide unit is disclosed in, for example, Japanese Patent Laid-Open No. 281154/1998, in which the separators to be interposed between any two adjacent rolling elements are made varied each other in their axial thickness to render unlike the pitches of the dents that might arise on the track rail, thereby to help ensure the slider moves smoothly with less noise. With this prior linear motion guide unit, many types of the separators, which are varied individually in axial thickness, are prepared previously and any desired type of the separator is selected depending on the interval between the adjacent rolling elements.
In another linear motion guide unit disclosed in Japanese Patent Laid-Open No. 126148/1993, in which the separators are also interposed between any two adjacent rolling elements, two types of separators are employed; many separators of a fixed axial thickness, and at least one of another type composed of halves adjustable relatively in position to make easy the production and assemblage of the linear motion guide unit. The separators are made less in size than the rolling elements and, therefore, the halves come to be produced in further small in size.
Japanese Utility Model Publication No. 10286/1976, moreover, discloses a ball bearing with separators, in which the separators interposed between the adjacent steel balls are each made with semi-spherical concavities that are less in the radius of curvature than the steel balls. In addition, the separators are elastic and also made with annular groove extending around the radially outer periphery thereof, thereby to allow freely adjusting the interval between any two adjacent balls.
Although but it may be considered to make the overall separator elastic, such separator is easily subjected to much deformation dependently on the force occurring between the adjacent rolling elements, so that the control of the interval between the adjacent balls becomes very complex. As will be seen from the above discussions, it may be worthwhile considering a recirculating-ball linear motion guide unit in which a separator is partly made ready to undergo elastic deformation so that the separator may not only absorb most variations in an interval between any two adjacent rolling elements with the deformation occurring in its elastic parts so far as the interval between the adjacent rolling elements remains within a preselected value, but also keep the interval between the adjacent rolling elements from becoming less than a preselected critical value, thereby making it possible to compensate for the variances in length of recirculating passages with the separator.
The present invention, therefore, has as its primary object to overcome the major problem in the prior linear motion guide unit where it is very tough to make a recirculating passage agree in length with a recirculating-ball string composed of rolling elements and separators disposed between any two adjacent rolling elements. More particular, it relates to a linear motion guide unit in which a separator is partly made ready to undergo elastic deformation so as to compensate for the variance in length of recirculating passage with the elastic performance, thereby making assembly operation easy and helping ensure smooth sliding motion with low noise.
The present invention is concerned with a linear motion guide unit comprising; a track rail having first raceway grooves on lengthwise side surfaces thereof; a slider riding astride on the track rail for movement in a sliding manner along and with respect to the track rail, the slider being made with second raceway grooves confronting the raceway grooves of the track rail; recirculating passages composed of load areas defined between the confronting first and second raceway grooves, and non-loaded areas formed in the slider to communicate with the load areas; rolling elements running through the recirculating passages; and separators disposed between any two adjacent rolling elements to move together with the rolling elements through the recirculating passages; wherein at least one of the separators is comprised of a major body allowing a minimum interval for the two adjacent rolling elements, and elastic supports arranged radially extended around the major body to keep the adjacent rolling elements apart away each other with a distance larger than the minimum interval.
With the linear motion guide unit constructed as described just above, when the force exerted on the adjacent rolling elements increases to make them even nearer each other, the separator is much subjected to elastic deformation to come into supporting the associated rolling elements at its major body, thereby keeping the adjacent rolling elements apart away each other with the allowable minimum interval. In contrast, as the force influencing the rolling elements to near each other becomes less, the elastic supports of the separator are restored by virtue of their own elasticity to their home position where the adjacent rolling elements are kept apart away each other with a distance larger than the minimum interval. Thus, it will be preferred that at least one of the prior separators in the recirculating passage is replaced with the separator of the present invention to automatically adjust the interval between any two adjacent rolling elements on the basis of the elasticity of the elastic supports, depending on the force exerted on the rolling elements.
In accordance with one aspect of the present invention, a linear motion guide unit is disclosed wherein the major body of the separator is of a cylindrical solid smaller in diameter than the rolling element and having axially opposing end faces confronting the adjacent rolling elements, the end faces being each made concaved with a radius of curvature, which is somewhat less than a radius of the rolling element. When the adjacent rolling elements have closed with the separator disposed between them, the separator supports the rolling elements with making contact with them, not throughout the concaved surfaces thereof but only at the annular peripheral areas of the concaved surfaces. Moreover, spaces left between the separator and the adjacent rolling elements may serve to accommodate therein lubricant. Thus, the separator may simply turn into either one of a supporting situation where it makes contact with the rolling elements at the areas reaching the annular peripheral areas around the concaved surfaces or another supporting situation where it comes into elastic contact with the rolling elements at only the elastic supports, depending on the contact pressure due to the rolling elements.
In accordance with another aspect of the present invention, a linear motion guide unit is disclosed wherein the elastic supports of the separator are each composed an elastically deformable leg connected to an outer periphery of the major body, and a seat attached to a radial distal end of the deformable leg to come into abutment against any one of the adjacent rolling elements under elastic influence of the deformable leg. The elastic force to make the seats urge the adjacent rolling elements apart away from each other is due to the elastic function of the elastically deformable legs arranged around the major body of the separator.
In accordance with another aspect of the present invention, a linear motion guide unit is disclosed wherein the seats on the elastic supports are each made with a concaved surface that is identical with the concaved end face of the major body in the radius of curvature. Moreover, the concaved surface of the seat is made coincident with a phantom curved elongation of the concaved end face of the major body when the associated deformable leg is free from any stress, thus recovering from their deformation. The elastic supports of the separator are each made with a curved surface equal in the radius of curvature with the concaved end face on the major body, which is somewhat less in the radius than the rolling element. The concaved surface on the elastic support is designed coincident with a phantom curved elongation of the concaved end face of the major body when the associated deformable leg is free from deformation. Thus, the rolling elements having made contact with the elastic supports approach each other whilst deforming the elastically deformable leg, till they come into contact with the annular peripheral areas of the concaved end faces on the major body, at which the rolling elements are kept apart away from one another with the minimum interval.
In accordance with a further another aspect of the present invention, a linear motion guide unit is disclosed wherein the elastically deformable legs are each made of a portion slim in thickness, which connects the associated seat to the periphery of the major body. The construction in which the leg is made slim in thickness provides the elastically deformable portion that may be easily subjected to elastic deformation with a bending force, to thereby allow the seat of the elastic support shifting with respect to the major body, thus resulting in moving relatively of the rolling element.
In accordance with another aspect of the present invention, a linear motion guide unit is disclosed wherein the elastic supports of the separator are positioned at desired intervals around peripheries of the axially opposing end faces of the major body, the end faces confronting the adjacent rolling elements. The elastic supports intermittent around the major body of separator are much flexible to deflect toward and away from the rolling element by virtue of the elastic deformation of the deformable legs, compared with the construction in which the elastic supports are formed continually throughout around the separator.
In accordance with another aspect of the present invention, a linear motion guide unit is disclosed wherein the elastic supports on the side facing any one of the two adjacent rolling elements are arranged offset circumferentially of the major body with respect to other elastic supports on the side facing another of the adjacent rolling elements. The construction in which the elastic supports confronting any one of the adjacent rolling elements are offset circumferentially of the major body relatively of the elastic supports on the side of another of the adjacent rolling elements allows the deformable legs to deflect or deform elastically with no mutual interference.
In accordance with a further another aspect of the present invention, a linear motion guide unit is disclosed wherein the elastic supports of the separator are each reinforced with a rib formed integrally with the major body. Although the elastic supports are subjected to repeated stress due to the rolling elements, the reinforcing ribs serve for protecting the elastically deformable legs from their premature deterioration, thus helping ensure the long-lasting separator.
According to the present invention, only one, two or more separator disposed between any two adjacent rolling elements in the recirculating passage may be sufficient to make the linear motion guide unit easy to assemble, because the separator of the present invention is formed in the construction easy to undergo the elastic deformation. In addition, at least one separator existing in the recirculating passage may be necessary to making it possible to compensate for the minute changes in interval between any two adjacent rolling elements to ensure the smooth movement of the slider in the common applications of the linear motion guide units.
For example, the separators each comprised of the major body and the elastic supports may be disposed everywhere between any adjacent rolling elements in the recirculating passage. In this case, the changes in the intervals between any two adjacent rolling elements can be compensated at every separator so that the slider is allowed to move far smoothly. As an alternative, the separators each comprised of the major body and the elastic supports may be disposed between the two adjacent rolling elements at only two locations, each to each location, where the recirculating passage is divided into just two halves.
In accordance with another aspect of the present invention, there is provided a linear motion guide unit in which the slider is comprised of a casing and end caps attached to lengthwise opposing ends of the casing, each to each end, the casing being made with the second raceway grooves and also having therein return passages to provide a part of non-loaded areas where the rolling elements is less subjected to load, and the end caps being made therein with turnarounds to provide other part of the non-loaded areas, communicating the load areas with the return passages to allow the rolling elements turning round in a recirculating manner.
With the linear motion guide unit constructed as described just above, the elastic supports of the separator are allowed to undergo easily the elastic deflection by virtue of the elasticity of the deformable legs. Moreover, the separator consisting of the major body and the elastic supports integral with the major body is easy in production. According to the separator of the present invention, the elastic supports to be abutted against the adjacent rolling elements are arranged at desired intervals around the periphery of the major body, with any elastic supports on the side of any one of the adjacent rolling elements being positioned offset circumferentially of the major body with respect to other elastic supports on another of the rolling elements. This construction allows the elastic supports making elastic deflection or deformation with no mutual interference.
Other objects and features of the present invention will be more apparent to those skilled in the art on consideration of the accompanying drawings and following specification wherein are disclosed preferred embodiments of the invention with the understanding that such variations, modifications and elimination of parts may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.